The most common ground condition which occurs at excavation sites is loose soil. In this condition, the typical shoring technique includes driving soldier piles into the soil to a level below the subgrade and, as the excavation proceeds, attaching wood lagging to the soldier piles to support the soil at the generally vertical face of the excavation. This vertical face also extends laterally along the side of the excavation. Tiebacks are also frequency connected to this type of a structure to provide extra support. Examples of such structures are illustrated in U.S. Pat. No. 3,490,242 issued on Jan. 20, 1972 to H. Schnabel, Jr. and U.S. Pat. No. 4,369,004 issued on Jan. 18, 1983 to Weatherby.
Another shoring technique, is disclosed in U.S. Pat. No. Re 28,997 reissued on Sept. 28, 1976 to Mason. In this technique, the earth mass of the embankment acts as a monolithic structure because an array of dowels functions to support the weight of the soil and to prevent the formation of slip planes. A skin of pneumatically blown concrete and reinforcing mesh is placed over the face as the excavation proceeds.
A shoring technique which is used in the unique ground condition wherein a rock underlayer is located below an earthen or soil overburden, is disclosed in U.S. Pat. No. 3,541,798 issued on Nov. 24, 1984 to H. Schnabel, Jr. The technique disclosed in the '798 patent includes a sheeting wall which bears against the overburden with vertically extending soldier beams having their bases abutting the underlayer; tiebacks extending downwardly and outwardly from the wall through the overburden and into the underlayer; and support members having a cross-sectional area substantially less than the smallest circle which would enclose the cross section of the soldier beams extending downwardly from the base of the soldier beams into the underlayer. This technique provides support for both the earthen overburden and the rock underlayer.
Another ground condition which is difficult to shore is soft shale or rock, or still soil. This type of ground is too hard to simply drive piles into, yet is too soft to be self supporting during excavation. The vertical face of an excavation therefore must be supported by some structure. Typically, this type of face is supported by a technique wherein relatively large holes are drilled, e.g. two to three feet in diameter; and soldier beams are inserted into the drilled holes and set in concrete. Thereafter, as the excavation proceeds, wood lagging is attached to the concrete columns. While this technique adequately supports soft shale, soft rock and still soil, the technique is expensive to use because of the large drilling equipment which is required and the relatively long time needed to drill the large diameter holes.
The present invention was developed to reliably support loose rock or shale, or stiff soil at the face of an excavation in a more economical and less time consuming manner than current commercial techniques.